Semiconductor devices such as transistors, diodes, thyristors, integrated circuits and the like are commonly made by the simultaneous processing of many identical discrete devices or integrated circuits in a common wafer.
A conventional wafer typically includes a semiconductive substrate. The substrate of a conventional wafer has a relatively high concentration of dopants (N or P), and correspondingly low resistivity. The surface resistivity across the top surface of such conventional substrates, however, is variable due in large part to the process used in the making of the ingots from which the substrates are obtained.
Semiconductor devices are typically formed on the top surface of a wafer. Generally, it is desirable to have uniform resistivity over the top surface of the wafer so that the devices formed in the wafer will exhibit substantially similar behavior. Typically, a layer of semiconductive material is epitaxially grown atop a surface of a substrate to obtain a semiconductive layer with uniform resistivity. The layer formed by epitaxial growth is conventionally referred to as an epitaxial layer or an epi layer. Epitaxial growth allows for better control of dopant concentration along the thickness of the epi layer, and thus better control over the resistivity of the epi layer.
There are substantial costs associated with epitaxial growth which increase the cost of the semiconductor devices.
It would, therefore, be desirable to eliminate the epi layer and still obtain a wafer that exhibits uniform resistivity on a top surface thereof in order to reduce the cost of semiconductor devices.